FIELD OF THE INVENTION
From one aspect, the present invention relates to a universal joint of the kind, hereinafter called the kind specified, normally referred to as a Hooke's joint and comprising two yoke elements which in use rotate about respective axes (hereinafter called the rotatry axes) and a connecting member connected to each of the yoke elements for pivotal movement about respective axes (hereinafter called the pivot axes) which are mutually perpendicular, the pivot axis of each yoke element also being perpendicular to the rotary axis of that yoke element, each yoke element comprising a base portion and a pair of arms projecting from the base portion in a direction longitudinally of the rotary axis, each yoke arm being formed with an opening in which a respective trunnion of the connecting member is received and the joint further including retaining elements associated with respective yoke arms for controlling movement of the associated trunnion relative to the arm in a direction away from the rotary axis.
Joints of the kind specified generally also include bearing cups situated one within the opening of each yoke arm to receive the associated trunnion of the connecting member, each bearing cup containing a plurality of needle bearings interposed between the trunnion and the peripheral wall of the cup. A form of retaining element which has commonly been used is a circlip. When such a retaining element is used, an annular groove to receive the circlip must be machined in the yoke arm adjacent to the outer end of the opening therein. Such groove can be formed by a turning operation, but it is difficult to control the position of the groove within close tolerances. Furthermore, the tool used in the turning operation is necessarily small and is liable to break.
A further problem which arises in this known construction is that the most satisfactory position for the groove is not known exactly at the stage when the groove is formed in the yoke arm. It is desirable that no substantial clearance should exist between the components in the assembled joint. If such clearances exist, relative movement of the components can occur after the joint has been assembled and it will not be possible to ensure that the joint remains balanced about the rotary axes during use. Such imbalance as may occur gives rise to vibration of the joint in use which gives rise to undesirable noise and may lead to excessive wear of components of the joint or associated members. It is not possible to manufacture the components of the joint economically to within very close tolerances and therefore if the position of the groove is determined before the components of the joint are assembled, in at least some cases, there will be undesirable play between components of the joint.
A further form of retaining element which has been proposed has a plurality of arms which project radially from the centre of the retaining element. With this further form of retaining element, it is not necessary to preform a groove in the yoke arm. The retaining element is inserted into the opening of the yoke arm from the outer end thereof and is forced into engagement with an end wall of the bearing cup. The arms of the retaining element are so formed that they deflect as the retaining element is forced into the opening and tend to bite into the wall of the opening when the retaining element moves in a direction away from the rotary axis.
This further known construction has several disadvantages. If the joint is disassembled for servicing purposes, it is difficult or impossible to ensure that, upon reassembly of the joint, the retaining element is returned to its original position. If the retaining element is fitted in a new position, it is likely that the reassembled joint will be unbalanced. Although if the retaining element is urged outwardly of the opening in the yoke arm by the adjacent bearing cup, the arms of the retaining element will bite into the walls of the opening and thereby oppose such outward movement, movement of the retaining element in the outward direction is not completely prevented. The resistance to outward movement reaches a value sufficient to prevent further outward movement of the adjacent bearing cup and associated trunnion only when there has occurred sufficient outward movement to cause the arms to bite deeply into the walls, of the opening. Accordingly, this form of retaining element cannot prevent play between components of the joint. Furthermore, the shape of the indentations made in the wall of the opening by the arms of the retaining element is such that the boundary of each indentation remote from the rotary axis is inclined at an obtuse angle to the adjacent surface of the wall of the opening. Abutment of the retaining element against this inclined surface does not provide secure retention of the retaining element within the opening and there is a risk that the retaining element will fail to remain in position throughout the service life of the joint.
It is an object of the present invention to provide a joint of the kind specified and a method of assembling such joint which reduces or overcomes one or more of the foregoing disadvantages.